Inflatable restraint systems configured for use as passive occupant restraint devices are now commonly utilized for impact protection. Modular driver air bag restraint systems are mounted on vehicle steering wheels which inflate during a collision in response to an electrical signal generated from one or more crash sensors mounted to the motor vehicle. The inflated air bag provides energy absorption for an occupant during a vehicle frontal crash. Additionally, the air bag improves the contact surface for the occupant with the vehicle interior during a frontal crash.
Currently, driver's-side air bag module assemblies utilize a cushion clamp ring equipped with a plurality of threaded studs to retain an air bag to the front face of a module base plate. An inflator is mounted to the back face of the base plate and extends through a central opening in the base plate so as to provide a passageway through which inflation gases are delivered to inflate the air bag during deployment. To assemble the module, the clamp ring is inserted inside the air bag cushion through the mounting opening, and the ring is seated about the inflator mounting opening so that the studs protrude through fastener apertures formed about the opening. The clamp ring studs extend outwardly from the air bag, and are used to attach the air bag to the module baseplate and the inflator. Typically, the ring, air bag, base plate, and inflator are bolted together by affixing a nut to the end of each stud. However, this technique requires the use of a large number of separate parts to construct the air bag module, thereby complicating its assembly.
Presently, a driver's-side module is mounted to a motor vehicle steering wheel hub with a plurality of fasteners. One variation utilizes a plurality of hollow and internally threaded studs which extend downwardly from the back of a module base plate, and which align with openings in the hub mounting plate of a steering wheel. Threaded fasteners are rearwardly inserted through the openings in the hub mounting plate and threaded into the studs on the module base plate. By tightening the fasteners, the air bag module is securely retained to the steering wheel hub. However, with this version it is necessary to individually thread all of the fasteners into a corresponding threaded stud in order to secure the module to the steering wheel hub. Likewise, all of the fasteners must be individually unthreaded in order to remove the air bag module from the steering wheel hub. Furthermore, the air bag must be separately retained to the base plate with a hub ring and dedicated fasteners.
In another version, a driver's side air bag module is retained to a vehicle steering column with spring clips. A plurality of tubular members downwardly extend from the hub portion of a steering wheel. A plurality of complementary mating cylindrical members likewise extend downwardly from the back of the module base plate for axial insertion into the tubular members in the hub. Aligned chordal or transverse slots are further provided in an aligned and interfitting manner in both the tubular and cylindrical members such that when assembled, the spring leg of a securement which is inserted into the respective slots releasably secures the cylindrical member against axial withdrawal from the cylindrical member. The securement mounts to the coaxial member as a result of the spring leg being biased into engagement with both members. To remove the air bag module from a steering wheel hub, a key is inserted into the bottom of the axial member which biases apart the spring leg to release the cylindrical member from within the axial member. However, with this design the air bag is still mounted to the base plate with a separate fastener ring and dedicated fasteners. Therefore, there is presently a need to reduce the number of parts necessary to construct a snap-fit driver's air bag module.